Excel (2010) Macro to extract string between semi colons

Try

Sub atest()
Dim LR As Long, i As Long
LR = Range("A" & Rows.Count).End(xlUp).Row
For i = 1 To LR
    With Range("A" & i)
        .Offset(, 1).Value = Mid(.Value, InStr(.Value, ";") + 1, InStrRev(.Value, ";") - InStr(.Value, ";") - 1)
    End With
Next i
End Sub